Which statement regarding the causes of intellectual disability is false?

Which statement regarding the causes of intellectual disability is false?
 
  a. The causes of mild intellectual disability are better understood than the causes of moderate to severe intellectual disability.
  b. There are over 1,000 different known organic causes of intellectual disability.
 c. Scientists cannot account for the cause of intellectual disability in the majority of cases.
 d. A genetic cause is known for almost three quarters of individuals with moderate intellectual disability.

Question 2

Children with intellectual disability have a greater chance of having ____.
 
  a. cystic fibrosis
 b. narcolepsy
 c. sensory impairment
  d. schizophrenia

Question 3

Generally, the emotional and behavioral problems of children with intellectual disability ____.
 
  a. constitute major psychiatric disorders
 b. are considered part of the spectrum of problems coexisting with intellectual disability
  c. often are not severe enough to require intervention
 d. have prevalence rates comparable to those of the general population

Question 4

Which psychiatric diagnosis is least common among children with intellectual disability?
 
  a. schizophrenia
 b. pica
 c. anxiety disorders
  d. mood disorders